Soil Classification and Evaluation of Preconsolidation Stress of Atlantic Outer Continental Shelf OCS Sediments from Oedometer and Cone Penetration Testing

Abstract

The geotechnical site characterization process typically begins with an assessment of the soil lithology, the in situ stress state, and the geostatic stress history of the formation, which involves identification of soil types and an evaluation of the preconsolidation, or effective yield, stress. The preconsolidation stress is defined as the maximum past stress physically and/or mechanically applied to the soil, representing the demarcation between normally consolidated (NC) and overconsolidated (OC) states. This paper presents an assessment of the preconsolidation stress of Atlantic Outer Continental Shelf (OCS) sediments within the zone of influence for offshore renewable wind turbine foundations, based on laboratory oedometer test data and cone penetration test (CPTu) data. Atlantic OCS sediments comprise a complex layering of clays, sands, and silts, classified using physical (textural) characteristics, including visual description, grain size distribution, and soil plasticity-based or CPTu data-based soil behavior type (SBT) charts. Soil classification for a variety of OCS sediment types from SBT charts, the Unified Soil Classification System (USCS), and ISO standard 14688-2 (2018) is compared and described. Predicted preconsolidation stresses are compared across several commonly used industry methods, and prediction accuracies are discussed in the context of soil type, minerology, and microstructure. Guidance is provided on appropriate site investigation (SI) techniques to allow characterization of these influential properties.